1. Field of the Invention
The present invention relates to an automatic anti-trap device, and especially relates to an automatic anti-trap device used on the power window of an automobile.
2. Brief Description of the Related Art
Transmissions comprised of a motor, gear module or screw are often used in daily life. These transmissions can facilitate such items as the power windows of an automobile, power gates, roller gates and conveyers. This kind of transmission has high output force and low power consumption to move a heavy object. But when the transmission works abnormally, such as when trapping an object or becoming blocked, the transmission is easily damaged and the trapped object is easily injured. Unless a person stops the transmission motion, the typical transmission, which does not have an automatic anti-trap device, can injure a person or damage an object by its high output force.
FIG. 1 is a functional block diagram of the automatic anti-trap device according to a prior art. This automatic anti-trap device comprises a micro processor 150, a driving circuit 130 and a position sensor 120. The driving circuit 130 and the position sensor 120 couple to the micro processor 150, and the driving circuit 130 and the position sensor 120 couple to the motor 110 separately. Furthermore, the micro processor 150 couples to a memory 170 to store the processed data. The motor 110 moves a window 199 (such as power window of an automobile) by coupling to a gear module 190. The micro processor 150 uses the position signals detected by the position sensor 120 to get time intervals and torques of the motor and compares the intervals and torques with the interval threshold value and torque threshold value stored in micro processor 150. When the time interval or torque is greater than the threshold values, the automatic anti-trap device stops or reverses the motor 110.
However, as time goes by, the physical condition of the device changes as the motor or machine ages. Hence, this kind of automatic anti-trap device easily exhibits error in action unless its threshold values are updated accordingly.
FIG. 2 is a functional block diagram of the automatic anti-trap device according to another prior art, which is different from that shown in FIG. 1 in that the position sensor 220 and the proximity sensor 225 of FIG. 2 are set at the border of the window 199 rather than coupled to the motor 110. The micro processor 250 makes logical judgments according to the information from position sensor 220 and the proximity sensor 225. This kind of device has an advantageous simple algorithm but is disadvantaged in that establishing the sensors and circuits at the border of the window 199 is difficult to design and costly to produce.
Therefore, an automatic anti-trap device is needed with updatable threshold values and is easily maintained and inexpensive to improve the transmission safety.